PREPARATION OF COLLODION MEMBRANES 557 



mark. Stop the watch whon tho nionisnis reaches the lower mark. Note the 

 interval of time. 



(c) Repeat the experiment, wanniiiii the hull) as in (a). 



(r/) Repeat as in (c). 



If the readings are reasonably consistent average them and calculate the 

 heat loss as in Chaj). XXXII. 



(e) Put on the silk thimble and repeat {((), {!>), (r) and (d). tSee text. 



PREPARATIONS 



76. Water for Faraday-Tyndall Phenomenon. 



Store a large volume of glass-distilled water in a paraffin covered jar 

 stoppered with a paraffined cork through which jiass two tubes, viz. a syphon 

 delivery tube reaching only one-third of the way down inside the jar, and an 

 air inlet tube protected by a plug of glass wool. The water should stand 

 undisturbed for at least three months before use. 



77. Collodions. 



Cellulose nitrate (gun-cotton or pyroxylin) is generally sold damped with 

 alcohol and, for very accurate work, should be dried before weighing. For 

 the following experiments this refinement is unnecessary. 



Acetic Aci<l Collodion. Four grams of commercial gun-cotton are placed 

 in a wide-mouthed glass-stoppered bottle of 200 c.c. capacity ; 100 c.c. 

 glacial acetic acid are added. The mixture is shaken gently until the gun- 

 cotton has dissolved, leaving no residue. The resulting sol is transparent 

 and will keep for weeks. 



Alcohol-Ether Collodion (Bigelow and Gemberling.) 7-5 c.c. of ethyl 

 ether are poured on .3 gm. of gun-cotton in a wide-mouthed stoppered bottle 

 as above. After 10-15 minutes, 25 c.c. of ethyl alcohol are added and the 

 mixture agitated until a clear solution is obtained. 



Either of these collodion solutions (after standing till free from bubbles) 

 may be used in the preparation of membranes. 



The permeability of collodion ineuibraues may be standardised for any 

 particular make of collodion by standardising the conditions under which they 

 are freed from ether and alcohol. Permeability can be increased by allowing 

 the collodion membrane to set in a moist atmosphere or under a bell-jar 

 whose content of air is saturated with alcohol, or, better still, acetone vapour, 

 before immersion of the fihn in water. Another and more reliable method of 

 attaining the same end is to add a less volatile constituent than ether and 

 alcohol to the stock solution, and, during the pre-immersion period, evaporat- 

 ing completely the volatile solvents in a dry atmosphere. The formula for 

 such a solution, due to Pierce, is as follows : Stock solution, 1 gm. nitro- 

 cellulose, X c.c. ethylene glycol, 25 c.c. absolute alcohol and enough anhydrous 

 anaesthetic ether to make 100 c.c. The permeability is controlled by varying 

 the amount (x c.c.) of the ethylene glycol from 0-5 c.c. for the least permeable 

 membrane (about 0-02 c.c. of water per cm." per min.) to 15 c.c. for a mem- 

 brane giving a filtration rate of about 0-5 c.c. per cm.^ per minute. 



78. Preparation of Collodion Membranes. 



Membranes are easily made in any size or shape, and, as they are trans- 

 parent, are very convenient for general use. They are, as ordinarily prepared, 

 unsatisfactory for the dialysis of whole blood or of bile. 



(i.) To cover a vessel siuular to a Grahcun diahjser. Cleanse a piece of 

 plate glass thoroughly and polish it. Pour sufficient collodion sol on the 

 centre of the plate to give a large enough membrane. Avoid bubbles. By 



